Dithiophosphate insecticides



United States Patent 2,884,353 DITHIOPHOSPHATE INSECTICIDES Donald L. Christman, Wilmington,

cules Powder Company, Wilmington, tion of Delaware No Drawing. Application August 30, 1955 Serial No. 531,610

10 Claims. (Cl. 167-22) Del., assignor to Her- Del., a corpora- S CHr-S(OR)2 S Hr-S(OR)2 in which each R represents a lower alkyl radical.

These organic dithiophosphate compounds have pesticidal properties and distinguish themselves from known pesticidal compounds in being more toxic at low concentrations toward certain pests and in having a much longer residual toxicity toward mites when sprayed on plants normally attacked by such pests.

The organic dithiophosphate compounds of this invention are made by reacting bis(chloromethyl) ether (1,3- dichlorooxapropane) with the desired diester of dithiophosphoric acid, the latter being the product of reaction of a lower aliphatic alcohol or a mixture of lower aliphatic alcohols of the formula ROH and P 5 The diester of dithiophosphoric acid may be reacted directly with the bis(chloromethyl) ether or it may be reacted in the form of its salt or in the presence of materials which sequester the hydrogen halide set free in the reaction.

The methods of making the products of this invention and methods of using the products as pesticides are more particularly described in the following examples in which all parts and percentages are by weight.

Example 1 To a solution of 30 parts of the ammonium salt of 0,0-diethyl dithiophosphoric acid in about 80 parts of acetone was added 9 parts of bis(chloromethyl) ether at room temperature. The precipitation of ammonium chloride began at room temperature and to complete the reaction, the mixture was heated to refluxing for 2 hours. Water was added to dissolve the inorganic salt and the product was extracted with benzene. After washing once with water, the benzene extract was dried over sodium sulfate and the solvent was removed under reduced pres- The residue was topped to '80/0.5 mm. leaving a light yellow viscous liquid consisting of 23 parts. This was oxapropane-l,3-dithiol S,S,-bis (diethylphosphorodithioate) which analyzed as follows: S, 30.7%; P, 15.0%; Cl, 0.3% compared to the calculated values of s, 30.8%; P, 15.6%; Cl, 0.0%.

An emulsiiiable concentrate of the residue was made by mixing 1 gram of the residue with 1 ml. benzene and '1 m1. sorbitan monolaurate polyoxyalkylene derivative (Tween 20). This concentrate was then diluted with Water to form dispersions of the residue in Water varying in concentration from 1.0% to *0.00025%. The dispersions were then tested for their toxicity to caged insects and to mites not-only by spraying theinsects but by spraying the plants alone as well for the purpose of determining residual toxicity. Standard tests methods were used for obtaining the results tabulated below.

Tests showed that a 0.1% emulsion of the composition of this example produced an kill of pea aphids when sprayed on pea plants infested with pea aphids.

A 1.0% emulsion gave a kill of southern army worms and a 0.1% emulsion gave an 80% kill of Mexican bean beetles. Residual activity tests were also run by spraying lima bean seedlings to run off with 0.1% aqueous emulsion and, after drying, infesting with twospotted mites after varying intervals of time. There resulted 90% mortality tothe mites after 26 days, the counts being taken 5 days after the infestation date.

Similar tests on residual activity to Mexican bean beetles with which lima bean seedlings treated at 0.1% concentration were infested showed 80% mortality in 2 days.

Example 2 0,0-dimethyl dithiophosphoric acid was produced by adding four molecular equivalents of anhydrous methyl alcohol to a suspension of one molecular equivalent of phosphorus pentasulfide (P 8 suspended in benzene while heating under reflux and venting the hydrogen sulfied evolved. The temperature was gradually raised to C. during the course of this addition and heating was stopped when hydrogen sulfide evolution ceased. The product was cooled and filtered and the solvent was removed at 80 C. under 15 mm. pressure.

To 40 parts of 0,0-dimethyl dithiophosphoric acid was added 80 parts benzene, and 16 parts pyridine. To the resulting solution was then added 14 parts bis(chloromethyl) ether and the mixture was refluxed for 6 hours. The resulting product was washed with water and then with dilute alkali, then with water and finally dried over sodium sulfate. After .removal of the benzene by distillation, a residue of oxapropane-1,3-dithiol S,S-bis (dimethylphosphorodithioate) amounting to about 22 parts was isolated.

This product was made into an emulsifiable concentrate by mixing 1 gram of the residue with 1 ml. benzene and 1 ml. sorbitan monolaurate polyoxyalkylene derivative (Tween 20). The resulting concentrate was then diluted with water to form dispersions of the residue in water of various concentrations. Toxicity data using the compound of this example showed 75% kill of pea aphids on pea plants with a 0.5% solution, and 90% kill of two-spotted mites with a 0.05% emulsion.

Example 3 0,0-Diisopropyl dithiophosphoric acid was prepared by the reaction of isopropyl alcohol on phosphorus pentasulfide and was then reacted with bis(chloromethyl) ether in benzene solution to produce oxapropane-1,3- dithiol S,S-bis(0,0-diisopropyl phosphorodithioate). This product was then made into a concentrate with benzene and Tween 20 and diluted to emulsions of various concentrations. These emulsions were shown to have high toxicity to insects and mites both by contact and by treating plants on which the insects and mites normally live.

Example 4 Dibutyl dithiophosphoric acid was prepared by the reaction of butyl alcohol on phosphorus pentasulfide and was then reacted with bis(chloromethyl) ether in benzene solution in the presence of pyridine to produce oxapropane-1,3-dithiol S,S-bis (0,0-dibutyl phosphorodithioate). This product was then made into a concentrate with benzene and Tween 20 and diluted to emulsions of various concentrations. These emulsions were shown to have high toxicity to insects and mites both by contact and by treating plants on which the insects and mites normally live.

The organic dithiophosphate compounds of the formula are those in which each R is the same or a different organic radical such as a lower alkyl radical: methyl, ethyl, n-propyl, isopropyl, isobutyl, sec-butyl and n-butyl. In the above definition of the scope of the compounds of this invention, lower alkyl is defined to include those alkyl radicals with 1 to 4 carbon atoms. The compounds which are especially effective as insecticides are those in which R is ethyl.

In producing the compounds of this invention the reaction between the bis(chloromethyl) ether and the ester of dithiophosphoric acid or its salt is carried out by heating the two reactants at a temperature at which reaction takes place but below the decomposition temperature in the range of 20 to 200 0, preferably in the range of 30 to 110 C. In order to get complete reaction it is preferable to use an excess over the theoretical amount of the ester of the dithiophosphoric acid.

When the reaction is complete, the excess ester of the dithiophosphoric acid is readily removed by washing with Water containing sutficient alkali to produce the watersoluble salt.

The reaction is preferably carried out in nonaqueous media in which an organic solvent is used as a diluent to aid in control of the reaction. Suitable solvents include benzene, toluene, xylene, cyclohexane, hexane, anhydrous alcohol solvents, acetone and dioxane. It is preferable to use acetone or aromatic hydrocarbon solvents when using an amine salt of the dithiophosphoric acid ester or when using an amine or ammonia as a sequestering reagent. After the reaction is complete, the solvent is readily removed by distillation.

When the diester of dithiophosphoric acid is used in the form of the acid in the reaction with the bis(chloromethyl) ether, hydrogen chloride which is liberated is preferably sequestered by adding a material to combine with the hydrogen chloride as formed. It is convenient to use pyridine for this purpose. However, in its place other tertiary organic amines may be used, and'they may be added in equivalent amount at the beginning of the reaction or gradually during the course of the reaction. Likewise, the amine can be reacted with the diester of the dithiophosphoric acid prior to carrying out the reaction with the bis(chloromethyl) ether as in Example 2. Amines which can be used include pyridine, tertiary alkyl amines such as trimethyl amine, tributyl amine, triamyl amine, dimethyl aniline and the like. Inorganic bases may also be used. These include ammonia, alkali metal hydroxides, carbonates and bicarbonates, and alkaline earth metal hydroxides and carbonates.

As in the case of organic bases, the inorganic bases may also be used first to form a salt of the ester of the dithiophosphoric acid. When the salt of the ester of dithiophosphoric acid is used as the reactant, it is preferable to use a salt which is soluble in the organic solvent used for the reaction. The organic salts of amines are particularly satisfactory because of the good solubility of these salts in the nonreactive hydrocarbon solvents. When the free acid is reacted with the bis(chloromethyl) ether, the alkaline material is preferably added gradually as needed but it can be added all at once if desired. Ammonia is suitably added gradually as a gas, the solids are suitably added in finely divided form.

The dithiophosphoric acid ester is produced by reacting the lower aliphatic alcohol, which is to form a part of the ester, With P 8 preferably in a nonreactive solvent sucha s benzene, toluene, xylene, hexane or cyclohexane and removing the H 8 which is liberated. The reaction is carried out at any temperature in the range of 50 to C., selecting the lowest practical temperature without decomposition. If different radicals are desired for the various R radicals, a mixture of alcohols may be used in the production of the dithiophosphoric acid ester. Likewise, dithiophosphoric acid esters produced from different alcohols can be mixed for use in the reaction with the bis(chloromethyl) ether.

The methods by which the products of this invention are isolated will vary slightly with the reactants used and the product produced. In some instances the chloride salt split out in the reaction separates and can be filtered off. In other instances the chloride salt is best removed by washing with water. The excess salt of the ester dithiophosphoric acid is also removed by the Water wash. The benzene or other solvent is then removed by distillation leaving an insecticidally active residue. Further purification by selective solvent extraction or by adsorptive agents such as activated carbon, or clays, can precede the removal of the solvent. Likewise, an organic solvent can be added to aid in the purification by adsorptive agents. However, the product is generally satisfactory for use as a pesticide without further purification.

The compounds of this invention are used as the sole toxic agent in pesticidal formulations or in admixture with other toxicants for modification of the properties of the individual toxicants. They may be used, for example, in admixture with toxaphene, DDT, Thanite, chlordane, rotenone, pyrethrin, and the like in many of the formulations suggested below.

The compounds of this invention are made into pesticidal compositions for use against insects and mites by dilution with an insecticidal adjuvant as a carrier therefor, by dispersing in an organic solvent, or in water, or by diluting with a solid insecticidal adjuvant as a carrier. Dispersions containing a surface-active dispersing agent have the advantage of spreading the toxic substance more effectively over the plant surface. Dispersions in organic solvents include dispersions or solutions in alcohols, pine oil, hydrocarbon solvents, difluorodichloromethane, and similar to organic solvents. The compounds of this invention are also used in aerosol formulations in which difluorodichloromethane and similar aerosol propellants form the propellant vehicle.

Aqueous dispersions are made up from the compounds of this invention, a surface active dispersing agent and water as the essential ingredients. The amount of the compounds of this invention in the aqueous dispersions when diluted for spraying of plants will be in the range of 10.0% to about 0.0001% of the aqueous dispersion.

Thev aqueous dispersion will ordinarily be made up "from a concentrate, and the concentrate will be dispersed in water to the proper concentration for application to the plants to be treated in the field. The concentrate is composed essentially of the compound of this invention and a surface active dispersing agent. The concentrate may also contain sufficient organic solvents to aid in effective dispersion. The amount of surface active dispersing agent used is usually at least 5% of the amount of toxic compound in the concentrate.

Suitable surface active dispersing agents for use in the compositions of this invention are those disclosed in Chemistry of Insecticides, Fungicides, and Herbicides, (Donald E. H. Frear, second edition (1948), pages 280-287) for use with known insecticides and include neutral soaps of resin, alginic and fatty acids and alkali metals or alkyl amines or ammonia, saponins, gelatins, milk, soluble casein, flour and soluble proteins thereof, sulfite lye, lignin pitch, sulfite liquor, long-chain fatty alcohols having 12-18 carbon atoms and alkali metal salts of the sulfates thereof, salts of sulfated fatty acids, salts of sulfonic acids, esters of long-chain fatty acids and polyhydric alcohols in which alcohol groups are ree,

clays such as fullers earth, China clay, kaolin, attapulgite, and bentonite and related hydrated aluminum silicates having the property of forming a colloidal gel. Among the other surface active dispersing agents which are useful in the compisitons of this invention are the omega-substituted polyethylene glycols of relatively longchain length, particularly those in which the omega substituent is aryl, alkyl, or acyl. Compositions of the toxic material and surface active dispersing agent will in some instances have more than one surface active dispersing agent for a particular type of utility, or in addition to a surface active dispersing agent, hydrocarbons such as kerosene and mineral oil will also be added as improvers. Thus, the toxic material may contain a clay as the sole adjuvant or clay and hydrocarbon, or clay and another surface active dispersing agent to augment the dispersing action of the clay. Likewise, the toxic material may have water admixed therewith along with the surface active dispersing agent, suflicient generally being used to form an emulsion. All of these compositions of toxic material and surface active dispersing agent may contain in addition synergists and/ or adhesive or sticking agents.

What I claim and desire to protect by Letters Patent is:

1. As a new composition of matter a compound of the formula 2. As a new composition of matter a compound of the formula I H our-snow),

in which R and R represent difierent lower alkyl radicals.

3. As a new composition of matter a compound of the formula II $Hr-SP (0 CH3): 1 i CHz-SP (0 CH3):

4. As a new composition of matter a compound of the formula H CHz-SP (0 C235):

I CHT'Si (O C2H5)9 5. As a new composition of matter a compound of the formula the compound the compound References Cited in the tile of this patent UNITED STATES PATENTS 2,494,126 Hoegberg Jan. 10, 1950 2,494,283 Cassaday et al Jan. 10, 1950 2,571,989 Schrader Oct. 16, 1951 2,586,655 Hook et al. Feb. 19, 1952 FOREIGN PATENTS 515,666 Canada Aug. 16, 1955 UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 2,884,353 April 28, 1959 Donald L. Christman It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, lines 18 to 22, claim 5, the formula should appear as shown below instead of as in the patent:

Signed and sealed this 25th day of August 1959 [SEAL] Attest:

KARL H. AXLINE, I ROBERT C. WATSON, Attestz'ng Ofiaer. f e COMissz'oner of Patents. 

1. AS A NEW COMPOSITION OF MATTTER A COMPOUND OF THE FORMULA
 6. A PESTICIDAL COMPOSITION COMPRISING THE COMPOUND OF CLAIM 1 AND AN INSECTICIDAL ADJUVANT. 